Process for hydrodesulfurizing and subsequently catalytically cracking gas oil



Feb. 9, 1960 J. A. ANDERSON, JR; ETAL 2,924,568 PROCESS FOR HYDRODESULFURIZING AND SUBSEQUENTLY CATALYTICALLY CRACKING GAS OIL Filed Feb. 28, 1955' GASOLINE FRAGT/O/VA no 5 ZONE L'-HAT/N6 0/L /0 I HYDRODE$U L- 2 D i FEED FuR/z4r/q/v y zom- Q 0 AND LIGHTER 2%;? Lemon/v5 6 c4 TALYT/a a CRACK/N6 v zo/vs I 7 iv:

PROCESS FOR HYDRODESULFURIZING AND SUB- ?)EigUENTLY CATALYTICALLY CRACKING GAS Application February 28, 1955, Serial No. 490,722

2 Claims. (Cl. 208-89) This invention relates to the production of high quality gasoline by catalytic cracking of relatively high molecular Weight hydrocarbons. The invention is particularly concerned with provision of low sulfur content catalytioally cracked gasolines. In accordance with this invention the feed stock to a catalytic cracking operation is subjected to a hydrodesnlfurization process with a desulfurization catalyst of improved physical characteristics in a manner providing marked advantages in the process and products of catalytic cracking.

.At fairly recent dates it has become appreciated that the sulfur content of gasoline is much more important than formerly thought. It has now been established that extremely low sulfur contents are desirable particularly in order to reduce what is called the octane requiremeat-increase of an engine. Gasolines which have been commonly used heretofore even though being considered to have satisfactory sulfur contents by the doctor test orv the like have been found to be characterized by a marked increase in the octane requirement of an engine after extended use of the engine. One of the factors found to contribute to this is the sulfur content of the gasoline.

it appears necessary and desirable to attain extremely low sulfur contents to avoid this problem. Attainment. of low sulfur content gasolines is again important in order to improve-the lead susceptibility of the gasoline to cause decreased engine wear and so on.

A potentially attractive process for attaining low sulfur content catalytically crackedgasolines is to first desulfurize the feed stock to the catalytic cracking operation. The feed stock is ordinarily the gas oil fraction of a petroleum crude oil boiling .inthe range of about 600 to 1000 F. or somewhat higher. The feed stock to catalytic cracking mayalso, be reduced crude petroleum or a tresidualhfraction such as a deasphalted residuum, boiling in.the range from about 800 F. and higher. While the sulfur content of such a cracking feed stock will yary depending upon its source, in general such stocks will contain about 0.2 to 3.0% sulfur and typically will contain about 2% of sulfur. Heretofore it hasnot been the practice to, desulfurize such feed stocks prior to catalytic cracking .With the result that during cracking sulfur pres'ent in feed stock is in part converted to constituents of the final catalytically cracked gasoline. In general, the sulfur content of a catalytically cracked gasolinewill be about -10% of the sulfur content of the cracking feed stock.

. One of the most attractive possibilities for economically desulfurizing catalytic" cracking feed stock employs the so-called hydrodes'ulfurization process. In this process the feed stock is contacted with hydrogen in the presence of a hydrogenation catalyst such as a cobalt molybdate catalyst supported on alumina. Effective desulfurizationof gas oil is possible in this manner. However, the possibility of processing a gas oil or higher boiling fraction in this manner prior to catalytic crack in; has never attained commercial usage because of se- States Patent 2,924,568 Patented Feb. 9, 1

vere debits resulting from theprocess. A particular difiiculty concerns the undesired hydrocracking of feed stocks during the hydrodesulfurization operation. This hydrocracking results in conversion of constituents of the feed stock' boiling in the gas oil boiling range to cracked constituents boiling below the gas oil boiling range. Specifically, hydrocracking during hydrodesulfurization results in the formation of gasoline and heating oil fractions. With reference ,to the gasoline formed during hydrocracking, this gasoline is of substantially the quality of virgin naphtha and consequently much inferior to the superior quality high octane number gasoline obtainable by catalytic cracking. It is 'app'an out then that any hydrocracking-occurring'during hydrodesulfurization of a crackingfeed stock effectively results in loss of valuable feed for catalytic cracking in a commercially expensive manner. It is, therefore, the particular object of this invention to provide a hydrodesulfurization process which will substantially reduce hydrocracking during the hydrodesulfurization of a feed stock to be subjected to catalytic cracking.

It may be noted that in addition to the formation of products lighter {than the feed due to hydrocracking, a 'small amount of lighter'rnaterial is formed due to the desnlfurization itself. That is, where "a sulfur atom is connected to two hydrocarbon radicals in a molecule, removal of the sulfur will convert themolecule into two lighter hydrocarbon fragments. The amount of lighter products formed in this manner is, however, relatively insignificant. V H V The general nature and objectivesofthis invention can be understood by reference to the following'specific data. In tests which were conducted to evaluate the production of catalytically cracked "gasoline from a hy drodesulfurized gas oil, "hydrosul furi'zation was carried out using an active commercial desul'fu'rization catalyst. The catalyst employed was aconventional cobalt molyb date catalyst supported on gamma alumina and activated at a temperature of about 1200 F. for a period of about 6 hours. This catalyst was employed to hydrode'sulfu'rize a heavy West Texas gas oil having" asulfur content or 1.6%. The hydrodesulfurization conditions were"0."15

v./v.7hr., 500 to 850 p.'s'.i.g., 735 to 750 F. and 6000 standard cubic feet of hydrogen per barrel. Inspection data of the gas oil fraction employed in these hydrodesulfurizatio'n experiments are given below:

During attainment of the desulfurized gas oil indicated, hydrocracking occurred resulting in the formation of 9.4

volume percent of naphtha and 16.6 volume percent of heating oil. segregating these fractions permitted a yield of 77.9 volume percent of the desulfuri'zed gas oil' characterized in Table I.

The desulfurized gas oil was then subjected to acatalytic cracking operation carried out by the fluidized solids technique. The cracking catalyst employed was a conventional silica alun ina catalyst and the conditions of.

cracking were conventional: '"In a first case the undesulfurized virgin gas oil employed in the above experiments was subjected to catalytic cracking, while in a second case the desulfurized gasoil referred to above was catalytically cracked. 'Surnmarizedbelow are the yields of products obtained by employing 'th'ese two feed stocks. These yields are compared "on the basis of constant carbon burning rate during the catalytic cracking operation;

Table II Direct Desulfn+ Cracking Cracking 43091; Conversion,Vol. Percent (Cat. Cracking .Only) 50. 57. 3 Yields, Percent on Feed:

- 1. Carbon, Wt. Percent..-; 1. 8 '1. 8 Dry Gas, Wt. Percen 7. 5. 8.0 Butylenes, Vol. Percent. 8. 7 9. 4 Butanes, V ol. Percent 3, 7 6. 8

0.430" r. Naphtha' Desulfurized, Vol. Percent 9.4 b Catalytic, Vol. Percent 37. 9 29. 1

Total Naphtha, Vol. Percent 37; 9 38. 4'ao-e5d F. Heating 011:

- Desulfurized, Vol. Percent 16. 6 Catalytic, Vol. Percent 13. 9 7. 9

v Total Heating Oil, Vol. Percent 13. 9 24. 5

650 F.+Cycle Stk., Vol. Percent 36. 1 25. 4

It will be observed from Table II that the undesired hydrocracking of the gas oil during hydrodesulfurization resulted in a substantial decrease in the amount of catalytically cracked gasoline obtainable. Thus, on desulfurization of thegas oil followed by catalytic cracking a yield of catalytic naphtha of only 29.1 volume percent was obtained. As compared to this, a yield of catalytic gasoline amounting to 37.9% was obtainable by the direct catalytic cracking of the undesulfurized gas oil feed. It

is apparent then that the conversion of gas oil constituents to. naphtha constituents during hydrodesulfurization resulted in reducing the yields of catalytic gasoline by an amount substantially equal to the gasoline formed by bydrocr acking. .u'Ihis factor is of great importance from a practical viewpoint because the gasoline formed during hydrodesulfurization by hydrocracking is greatly inferior to eatalytically cracked gasoline. For example, the hydrocracked gasoline obtained as indicated above only had a CFR research number of 69.7 when tested with 1.5 cc. per gallon of tetraethyl lead. As compared to this, the catalytic gasoline obtained as indicated has a CFR research number of 98.6 when tested with 1.5 cc. per gallon of tetraethyl lead. It must be appreciated then that the hydrocracked gasoline formed during a hydrodesulfurization operation is of such unsuitable quality that the amount of this gasoline formed must be considered a debit for the process. 1. i

In other words, as brought out, in a combination process involving hydrodesulfurization of a gas oil followed by catalytic cracking of the gas oil it becomes importantv to minimize hydrocracking during the first step. As pointed out, gasoline formed during desulfurization is of such poor quality that the formation of this gasoline results in the substantial loss of equivalent amounts of catalytically cracked gasolines. Another way of considering this is to appreciate that from a given gas oil feed stock a certain amount of gasoline can be obtained. Because of the superior gasoline obtainable by catalytic cracking, it ismost attractive that all gasoline conversion be achieved by catalyticfcracking. It is the particular r 4 feature of this invention to provide a process which will permit the substantial attainment of this goal.

The present invention is based in part on the discovery that particularly effective catalysts for the hydrodesulfurization of gas oil and heavier oils can be provided by controlling the physical characteristics of conventional porous solid desulfurization catalysts to maintain the following values: (1), A most frequent pore diameter (D,) of the catalyst of at, least about 60 Angstrom units and no greater than about 400 A. Preferable. values are in the range from 75 A. to 200 A. (2) A spread of at least about 10 A. in the range of the more frequent pore diameters (AD the spread is preferably in the range from 10 A. to 200A. (3) A pore size distribution factor,-

- gamma. -+10 of at least about 5, and preferably above 10.

The methods of determining D AD and PD factor, and methods of preparing'porous catalysts having controlled physical characteristics in-the ranges set out above are described in detail'in co-pending application Serial No. 490,732, now US. Patent No. 2,890,162, entitled Improved Porous Contacting Agents and Use Thereof, filed of even date herewith in the names of James A. Dinwiddie, Max A. Mosesman, James A. Anderson, Ir., and Lonnie W.,Vernon,"the-disclosures of which are made a part hereof.

The chemical nature of the preferred catalyst for the hydrodesulfurization step of the present invention is, as described above, cobalt molybdate on alumina. This also embraces compositions of non-stoichiometric proportions of mixed oxides of cobalt and molybdenum on an alumina base. Such catalyst compositions are Well known to the art. It is essential for the successful practice of the present invention that the hydrodesulfurization catalyst have the physical characteristics set out above. Catalysts of other compositions than cobalt molybdate on alumina may suitably be employed, provided they have the physi- 7 other suitable supports such as zirconia or boria-alumina.

A preferred catalyst for use in the desul furization step of'the' presentinvention may be prepared from conventional cobalt molybdate on alumina catalysts by heating these catalysts for a period in the range from about 7 4 to 36 hours at temperatures in'the range of 1350 to 1550 F. .A preferred range is between 1400 and 1500 F. It is to be understood that this particular heat treatment is carried out in addition to those conventionally applied to such catalysts during catalyst preparation. The results obtainable by heating the catalysts at the above defined conditions are not obtainable even atprolonged heating periods at temperatures in the conventional activation, range of about 1000 to .1200 F.

Activation of these catalysts at temperatures above 1350 F. for periods of about 4 to 36 hours results in a substantial change in the physical characteristics of the catalysts. It has been established that the principal physical-=changes involve a substantial increase in the size of the most frequent pores of the catalyst and also a substantial broadening of the range in predominant pore sizes. Basic work has also established that thesechanges in physical properties markedly improve the activity and other catalytic properties of these catalysts.

A cobalt molybdate on alumina catalyst with the stated physical characteristics has been found to be particularly satisfactory for the hydrodesulfurization of feedstock for catalytic cracking: The special prt'ape'rti'es of'the' catalyst result in substantially minimizing the undesired hy-' drocracking ordinarily occurring during hydrodesulfurization. These properties of the catalysts are further uti- The g'as-oi1 designated as feedstock'No. 1"was-'thei-1* hydrodesulfurized in separate runs, employing catalysts A, B and C respectively, at a temperature of 765 F., a pressure of 400 p.s.i.g., a hydrogen feed rate of 6000 lized in accordance with this invention by employing 5 standard cubic feet per barrel, and several space velocities. particular temperatures of hydrodesulfurization and by Pertinent data regarding the catalysts and the hydrodeconducting the process at particular rates'of throughput. sulfurization operations are shown in Table IV:

Table IV Catalyst, A B 0 1196691124 Hrs. at 13.- 1,100 1,400 1,600 A 35 60 114. AD3,A 10 as 12 B1) Factor 1 14 16- Conditions: 1

FeedRate r .64 1.10 .24 .65 1.12 1. 73 .25 .73 1.1 Hgloilratio,s.e.t'./bbl 6,810 6,870 5,790 6,520 6, 090 6, 450 6,010 5,820 6,230 Reactor Temperature, 7 765 765 76 765 765 765 765 765 Liquid Yields and Inspections:

Vol.Percent Yield- 3 Gasoline (boiling below 430 13.5 8.0 6.5 12.5 9.0 6.0 6.5 9.5 6.8 3.5 HeatingOil (boiling 430-580F 14.0 9.0 17.5 12.5 12.5 8.0 14.5- 1 9.7 I 10.0 Gas 011 77.6 83.2 67.9 77.9 79.8 8616 76.1 f 82.0 1 85.5 99.2 99.5 98.7 97.9 99.4 98.3 100.1 99.1 98.5 99.0

Wt. Percent Sulfur in liquid 0. 04 0.10 0.17 .02 .06 .10 .16 .05 .09 .13" Sulfur removal, percent 97 94 90 99 1 97 94 91 9s 95 1 90 These and other features of the invention will be estab- Itwill be noted from the datain Table IV that. activalished by the examples and data which follow. tion of a cobalt molybdate type catalyst at. temperatures, In a first series of studies to evaluate the principles in the range of 1400" F. and higher results in catalysts of this invention, separate portions of a cobalt molybhaving increased D AD and pore distribution factors, date type catalyst supported on low silica granular gamma and improved properties for a hydrodesulfurization procalumina were subjected to activation at temperatures in ess. In particular it will be observed that activation; the broad range of 1100 to 1500 F. for a period of 24 at the high temperatures indicated causes a substantial hours. The catalyst employed contained 15% of cobalt increase in the hydrodesulfurization activity of the catarnolybdate and was pilled in the form of inch pills lyst, indicating the permissible use of substantially higher employing 3% graphite as a pilling aid. Prior to the throughput rates while attaining the same levels of. desul-- extended activation at temperatures in the range lndifurization. Again the extent of hydrocracking. encountcated .this catalyst had been activated by treatment at ered during hydrodesulfurization is shown to be critical- 1200 F. for 6 hours. The portion activated for 24 1y affected by the change in physical characteristics of hours at 1100 F. is hereafter referred to as catalyst A, the catalyst. This is particularly shown by the data of. that heate at as catalyst and that heated at Table IV with reference to the volume percent of: gaso 5 as ly These catalysts wefe mployed line yield. Thus, for example, at feed rates of about. 9. hydrodesulfunze a West Texas gas 1 deslgnated as 1 v./v./hr. approximately 6.5 of constituents are cone ifl d $9 1 r s mspectlons shwn m Table verted to gasoline boiling range products by catalyst A, which was activated at 1100 F. and had a D; of less Table II than 35 A., AD of less than 10, and pore distribution factor less than 1. However, for catalyst C, activated Feed stock 1 at 1500 F and having a. D: of 119 A AD of 12 and 1.72 2.10 R bi igit'yfiifff 24.1 24.4 pore distnbutlonafactor of. 16, only about 3.5% of such Dlsnnatwnm- ASTM ASTM conversion occurred. It is apparentthen that a catalyst 10 mm mm of increasedpore size, pore size range, and pore distribu- Atmqg Oomctd Gas 011 Corrected tion factor, such as the severely activated cobalt molyb- Pherlc zg Engler 3 date catalyst, permitsattainmentof increased desulfurizagas oil designated as feedstock No. 1, supra. The hydrodesulfuriz-ation processes were conducted. at liquid space velocities of about 4.5 v./v./hr. at a; pressure of 400 p.s;i.g. using about 6200 standard cubic; feetof hydro gen. per. barrel of. feed and. employing. astemperatures 17 of operation 765 and 797 F. The data obtained; in. these runs are summarized in table V-A:

8i -It-will be-obs'erved-from the data in Table V-B that under the conditions of pressure and space velocity employed, the operating temperature didafrect the degree of desulfur'ization. Substantial desulfurization was ob,-

Table tained at a temperature of 605 and higher. It will be further observed that the amount of gasoline produced, Feed Stock No.1 indicated by the percent of liquid product distillable at gif ff, 430 F., increased from 1% at 605 F. to 5% at 749 ADB 1 F.; the amount of light heating oil produced indicated PD Facwr" 16 by the percent of product distillable between 430 and 580 F. less the 5% contained in the feed, increased from *g; f$ ;f M7 M6 5% at 605 to 8% at 749: F.; and the net change in i/ s. 6,200 6,222 the amount of heavier heating 011 lndicated by the per- ,fif zggg gfgf' $8; cent of product distillable between 580and 650 F. less Liquid Pr0d11 ct Yie lds and Inspections: .15 the 17% contained in the feed, increased from a net disltgfigt ggg ggr Y appearance of 5% at 605 F. to a net increase of 2% at at430 1.5 2g 749 F 1 a 7 3i 523w 2: II .1523 Further Comparing he r s nif s -A and 33 P850611; sufiginllitquid g; 33 the following may be noted: The reaction condition for move men the runs in Table V-B, including a lower space velocity, higher pressure, and lower hydrogen. to oil ratio, were somewhat more severe than those in Table V-A. The It will be observed from the data in Table V-A that catalysts were chemically identical, had received similar the temperature of operation between 765 and 797 F. heat treatment and had similar pore distribution chardid not significantly afiect the extent of desulfurization, acteristics, but were dissimilar in that catalyst C was in but that the amount of gasoline produced, indicated by the form of Va" x /s" pills and catalyst D was in the the percent of liquid product distillable at 430 F., inform of 10-20 mesh particles. It is believed that the creased from 1.5% to 5%, and the amount of light catalytic effects of catalysts C and D were substantially heating oil, distillable from 430 F. to 580 F., increased identical. The feed stocks were chemically similar, befrom 6% to 9%, as the temperature was increased. ing fractions of West Texas Crude, but feed stock No. 2 The second set of runs was made at temperatures in had a somewhat higher concentration of lower boiling the range from 507 F. to 749 F. The catalyst emcomponents than feed stock No. 1. ployed, designated as catalyst D, was a cobalt molyb- The data in Tables V-A and V-B indicate that at the date on alumina catalyst prepared from a commericalconditions and with the catalysts shown, substantial (10? type catalyst containing approximately 15 weight percent s'ulfurization of gas oil is obtained at temperatures in cobalt molybdate supported on substantially silica free the range from 600 to 800 F., and that cracking of alumina, in the form of Mt inch pills, which had been the gas oil is substantially reduced or almost totally inheat-treated for six hours at 1200 F., ground, and rehibited at the lower temperatures in that range, especially pilled as ,41" x Vs" pills. The x /8" pills were between 600 and 765 F. heated in the presence of moving air at a temperature Additional runs were carried out in which gas oil feed of 1500 F. for 24 hours followed by crushing and stock No. 1 was hydrodesulfurized with catalyst C at screening to obtain catalyst D in the form of 10-20 765 F., 400 p.s.i.g., with a hydrogen rate of about 6000 mesh particles. The feed stock employed was a West s .c.f./bbl. but in which the throughput of the operation Texas Gas Oil designated as Feed Stock No. 2, the inwas varied in the range of about 0.5 v./v./hr. to about spections of which are given in Table III. 4.5 v./v./hr. In these experiments it was found that 'Ihe hydrodesulfurization processes were conducted at the amounts of hydrocracking occurring during hydro liquid space velocities-of about 2 v./v./hr., at a presdesulfurization is very greatly affected by the throughsure of 800 p.s.i.g., using about 2100 standard cubic put rate. It is apparent, of course, that the extent of feet of hydrogen per barrel of feed, and employing varidesulfurization is also affected by throughput rate but ous temperatures of operation in the range from 500 the significant fact discovered was that the extent of to 750 F. The data obtained in these runs are sumhydrocracking could be substantially decreased at higher marized inTable V-B. throughput rates without greatly afiecting the degree of Table V-B Feed Stock No. 2 Cataly D DI AD= 30 P1) factor 24 Conditions:

. Space Velocity, v./v.lhr 2 2 2 2 m on ratio, s.c.f.lbb1- 2,100 2,100 2,100 2,100 2,100 Reactor Pressure, p.s.i. 800 800 800 800 800 Avg. Reactor Temp., 507 605 652 677 749 Feed Engler .Distillatton Vol. percent ofl v at 430 F trace trace 1 2 2, 5 5 7 11 12 12 18 at 650 F 22 23 23 v 27 so 31 wt. Percent Sulfur in Liquid 2.10 1.81 1.18 0.57 0.28 0.07 Sulfur Removed, Percen '14 44 73 87 -97 9 hydrodesulfurization. This efiect is particularly indicated by the data shown in the following table:

As developed, therefore, the process of this invention concerns the hydrodesulfurization of a gas oil or heavier essentially hydrocarbon fraction to be used as a catalytic cracking feed stock under the following specific conditions: the catalyst employed is a porous solid desulfurization catalyst having a most frequent pore diameter, D, of at least 60 A. and preferably in the range from 75 A. to 200 A. a spread in more frequent pore diameters, AD of at least about A. and preferably between 10 A. and 200 A. and a pore distribution factor, PD, of at least 5. The throughput employed is to be in the general range of about .5 to 6 v./v./hr. and preferably well above 1 v./v./hr., e.g. in the range from 2 to 4.5 v./v./hr. The amount of hydrogen employed may be chosen from the range of about 1000 to about 6500 cubic feed per barrel depending in parton the sulfur content and nature of the feed stock to be hydrodesulfurized. The hydrogen rate may be specifically about 6000 standard cubic feet per barrel. The temperature of hydrodesulfurization will be chosen from the range of about 600 to 800 F. but in the preferred practice of this invention the temperature will be specifically chosen in the range of 600 to 765 F. Pressures employed in the hydrodesulfurization step will be in the range from about 200 to about 1000 p.s.i.g., and preferably will be between 400 and 800 p.s.i.g.

Considering the data which has been presented, the unique advantages of this invention can be appreciated and the basic nature and advantages of this invention are clearly established. Thus, from the data which have been referred to, when a gas oil is subjected to conventional hydrodesulfurization and then catalytically cracked, 29.1 volume percent of catalytic gasoline in obtainable with 9.4 volume percent of hydrocracked gasoline. However, by using the process of this invention to hydrodesulfurize this gas oil prior to catalytic cracking, while substantially the same amount of total gasoline will be obtained, only about 2.3 volume percent of hydrocracked gasoline will be obtained. It is apparent then that the process of this invention permits the marked increase in the amount of catalytically cracked gasoline obtainable at octane levels above about 90 CFR research. It may also be observed that the process of this invention minimizes the formation of heating oil during the desulfurizatiou operation in a manner contributing to better product distribution of the catalytically cracked gas oil. These and other advantages are achieved while substantially employing the catalytic cracking process because of the higher quality feed stock employed. In this connection, for example, the hydrodesulfurization process of this invention provides a cracking feed stock low in Conradson carbon, reducing the undesired carbonization of the cracking catalyst. Again as indicative of the superiority of this feed stock, the cycle oil obtained in the catalytic cracking operation is of substantially higher value for use in recycle catalytic cracking.

The feed stock will be desulfun'zed in zone 1a accord-' ing to the particular principles referred to hereinbefore. The hydrodesulfurized products removed from zone 1a through line 2 may be passed to a fractionator 3 permitting segregation of the small percentage of lighter constituents resulting from hydrocracking of the feed stock. Thus, fractionator 3 may be operated to permit removal of the gasoline fraction through line 4 and of a heating oil fraction through line 5. The segregated topped cracking feed stock will then be removed as a bottoms product through line 6 for introduction to eatalytic cracking zone 7.

The cracking operation carried out in zone 7 may be of any desired conventional type. Thus, the catalyst may constitute material such as modified natural or synthetic clay or gel type catalysts and particularly active clays, silica-alumina, silica-magnesia compositions or other cracking catalysts. ous or batch nature employing fixed beds, moving beds, fluidized or suspensoid systems. The cracking is carried out at temperatures of about 800 to 1000 F. and pressures of about atmospheric to 25 p.s.i.g. or higher.

Cracked products removed from zone 7 through line 8 are fractionated in the product fractionator 9. Fractionator 9 may be operated to permit removal of C and lighter constituents through overhead line 10, gasoline through line 11 and higher boiling fractions through the lower side stream withdrawals 12, 13 and so on and bottom withdrawal 14.

In the practice of this invention the gasoline segregated from line 4 of the process illustrated is obtained In order to fully indicate the practical application of this invention, reference is made to the accompanying drawing which diagrammatically shows a flow plan embodying the invention.

In this drawing an essentially hydrocarbon feed stock of gas oil boiling range or heavier is first introduced by line 1 to a hydrodesulfurization zone identified by 1a.

in relatively low amounts. This is also true of the heating oil obtained in line 5. The low yield of gasoline and heating oil from this portion of the process is the particular feature of this invention resulting from conduct of the hydrodesulfurization zone in the manner particularly indicated. Because of the extremely small amounts of hydrocracking occurring during hydrodesulfurization it becomes practical to simplify or even eliminate the fractionation requirements of the process. Thus, in this connection fractionator 3 can constitute a simple splitter in which gasoline is removed overhead and heavier products, including heating oil and gas oil, are removed as a bottoms stream. This bottoms stream includes the heating oil of line 5, and the gas oil of line 6 may be passed directly to catalytic cracking zone 7 without necessity for further fractionation. In addition, it is possible to pass products of the hydrodesulfurization zone 1a directly to a catalytic cracking operation without any intermediate fractionation. Inclusion of the hydrocracked gasoline and heating oil in the catalytic cracking zone primarily results in decreasing the capacity of the catalytic cracking zone. While this decrease would be practically intolerable in the case of conventional hydrodesulfurization operation, in the practice of this invention sufficiently small portions of hydrocracked products are formed during hydrodesulfurization so as to make this practicable.

What is claimed is:

1. A process for maximizing the yield of catalytically cracked gasoline of low sulfur content and high octane from a gas oil feed stock and for minimizing the yield of low octane number hydrocracked gasoline which comprises the steps of hydrodesulfurizing a feed stock boiling in the range between about 600 and 1000 F. and comprising a sulfur-containing crude petroleum hydrocarbon in the presence of a catalyst consisting essentially of cobalt molybdate supported on substantially silicafree gamma alumina under hydrodesulfurization c0nditions including a pressure within the range of about 400 to 800 p.s.i.g., a temperature within the range of about 600 to 765 F., a space velocity within the range of 2 to 4.5 volumes of feed per volume of catalyst per hour and a hydrogen charge rate within the range of 1000 to 6000 cubic feet of hydrogen per barrel of feed stock, said catalyst having been activated at a temperature with- The operation may be of a continuin the range of about 1400 to 1500F. for a period of about 4 to about 36 hours and having a most frequent pore diameter within the range of about 75 to 200 A., a spread in the more frequent pore diameters within the range of about 10 to 200 A. and a pore distribution factor of more than about 10 and thereafter catalytically cracking at least the gas oil fraction of the products of said hydrodesulfurization reaction to obtain said catalytically cracked gasoline.

H 2. A process as in claim 1 wherein the said catalyst consists essentially of about 15 weight percent of cobalt molybdate and about 85 weight percent of gamma alumina.

References Cited in the file of this patent UNITED STATES PATENTS Ocon Mar. 18, 1941 Conn Aug. 8, 1944 Smith et a1 June 17, 1947 Claussen et al. Dec. 9, 1947 Ashley Oct. 27, 1953 Rosset et al. Mar. 9, 1954 Porter et al Aug. 10, 1954 Brown Dec. 14, 1954 Engel et al Dec. 21, 1954 Miller et a1. Feb. 7, 1956 

1. A PROCESS FOR MAXIMIZING THE YIELD OF CATALYTICALLY CRACKED GASOLINE OF LOW SULFUR CONTENT AND HIGH OCTANE FROM A GAS OIL FEED STOCK AND FOR MINIMIZING THE YIELD OF LOW OXTANE NUMBER HYDROCRACKED GASOLINE WHICH COMPRISES THE STEPS OF HYDRODESULFURIZING A FEED STOCK BOILING IN THE RANGE BETWEEN ABOUT 600* AND 1000*F. AND COMPRISING A SULFUR-CONTAINING CRUDE PETROLEUM HYDROCARBON IN THE PRESENCE OF A CATALYST CONSISTING ESSENTIALLY OF COBALT MOLYBDATE SUPPORTED ON SUBSTANTIALLY SILICAFREE GAMMA ALUMINA UNDER HYDROESULFURIZATION CONDITIONS INCLUDING A PRESSURE WITHIN THE RANGE OF ABOUT 400 TO 800 P.S.I.G., A TEMPERATURE WITHIN THE RANGE OF ABOUT 600 TO 765*F., A SPACE VELOCITY WITHIN THE RANGE OF 2 TO 4.5 VOLUMES OF FEED PER VOLUME OF CATALYST PER HOUR AND A HYDROGEN CHARGE RATE WITHIN THE RANGE OF 1000 TO 6000 CUBIC FEET OF HYDROGEN PER BARREL FO FEED STOCK, SAID CATALYST HAVING BEEN ACTIVATED AT A TEMPERATURE WITHIN THE RANGE OF ABOUT 1400* TO 1500*F. FOR A PERIOD OF ABOUT 4 TO ABOUT 36 HOURS AND HAVING A MOST FREQUENT PORE DIAMETER WITHIN THE RANGE OF ABOUT 75 TO 200 A., A SPREAD IN THE MORE FREQUENT PORE DIAMETERS WITHIN THE RANGE OF ABOUT 10 TO 200 A. AND A PORE DISTRIBUTION FACTOR OF MORE THAN ABOUT 10 AND THEREAFTER CATALYTICALLY CRACKING AT LEAST THE GAS OIL FRACTION OF THE PRODUCTS OF SAID HYDRODESULFURIZATION REACTION TO OBTAIN SAID CATALYTICALLY CRACKED GASOLINE. 